Rotary kiln with built-in heat exchanger



May 29, 1962 N. E. ANDERSEN ROTARY KILN WITH BUILT-IN HEAT EXCHANGER 3 Sheets-Sheet 1 Filed April 14, 1960 FIG.2

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ROTARY KILN WITH BUILT-IN HEAT EXCHANGER Filed April 14, 1960 5 Sheets-Sheet 2 J i W FIGJO FIG.9

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May 29, 1962- N. E ANDERSEN 3,036,822

ROTARY KILN WITH BUILT-IN HEAT EXCHANGER Filed April 14, 1960 5 Sheets-Sheet s United tates 3,036,822 ROTARY KILN WITH BUILT-IN HEAT EXCHANGER Niels Edvard Andersen, Copenhagen-Valby, Denmark, assignor to F. L. Smidth & Co., New York, N.Y., a corporation of Delaware Filed Apr. 14, 1960, Ser. No. 22,283 Claims priority, application Great Britain Apr. 15, 1959 6 Claims. (Cl. 263-32) This invention relates to rotary kilns of the type used for burning cement raw materials, limestone, and ores and having their interior divided for a part of its length into longitudinal compartments by radial partitions. More particularly the invention is concerned with kilns of the stated construction, in which the compartments are formed by novel partitions means not subject to damage as a result of the deformation which the kiln undergoes during rotation.

In rotary having longitudinal compartments, the material to be burned moves counter-current to the gases flowing through the kiln and absorbs heat directly and indirectly from the gases. As the material travels through the compartments, it is divided by the partitions into smaller streams so that its free surface is increased and it is better able to absorb heat from the gases and the partitions. The partitions, accordingly, act as a built-in heat exchanger and are commonly so called. Such a heat exchanger is usually located within the first third of the kiln at the material feed end with the inlet of the heat exchanger lying at a point where the raw material contains little or no moisture.

Heretofore, the partitions used in forming the compartments in a kiln have been made either of heat-resistant steel or of heat-resistant non-metallic materials and, in particular, of the ceramic material chamotte. Steel partitions have high mechanical strength but, if placed too far down the kiln, they are liable to be injured fairly quickly by the heat, so that they require total or partial replacement. It is desirable that the heat exchanger extend a substantial distance down the kiln to insure the greatest possible efficiency of heat exchange but the use of steel partitions restricts their location in the kiln with resultant loss of some of the advantages of a heat exchanger in the kiln.

Partitions of ceramic material may be extended farther down the kiln without being quickly burned out but such partitions as made heretofore are subject to damage when exposed to the heavy compressive and tensile stresses resulting from the deformation of the kiln taking place during its rotation. Such deformation of the kiln is caused by gravity, the weight of the kiln and the charge, and thermal action and causes the shell, which is of substantially cylindrical form, to assume a slightly elliptical cross-section with its greatest dimension horizontal. Deformation resulting from thermal action is particularly pronounced when ceramic partitions are used because the coefficients of thermal expansion of the shell and partitions are different. The effect of stresses set up by the deformation is to cause damage to the partitions, shortening their life and requiring total or partial replacement.

The present invention is directed to the provision of a rotary kiln having a built-in heat exchanger formed by partitions of ceramic material connected to the kiln shell by resilient connections so that the partitions are enabled to withstand without damage the stresses applied thereto by the deformation of the kiln shell occurring during operation. The partitions meet at the kiln axis and extend radially therefrom and the connection between each partition and the shell includes a member extending through E Patented May 29, 1962 the shell and engaging the outer end of the partition. Outside the shell, the member is acted on by a spring which causes the member to exert a compressive force on the partition urging it toward the kiln axis. Each partition may be made of a single piece of ceramic material but is preferably formed of a stack of ceramic blocks held in face-to-face contact by the compressive force applied to the partition. Each partition is, in effect, a crossloaded column and it has been found that only a relatively light spring load, far less than the ultimate breaking stress of the blocks, is sufficient to maintain the partitions against collapse. As the springs acting on the partitions are outside the kiln shell and not exposed to the heat within the kiln, the springs are of long life. Accordingly, the only parts subject to replacement are the members, which may be of simple design and can be made of heat-resistant metal to prolong their life.

For a better understanding of the invention, reference may be made to the accompanying drawings, in which FIG. 1 is a fragmentary transverse cross-sectional view of a rotary kiln equipped with a built-in heat exchanger constructed in accordance with the invention;

FIG. 2 is a sectional view on the line 2-2 of FIG. 1;

FIG. 3 is a view in perspective of one of the blocks used in forming a partition of the heat exchanger;

FIG. 4 is a sectional view on the line 44 ofFIG. 3;

FIG. 5 is a fragmentary end view of the central part of the heat exchanger showing the curvature of the contacting faces of the blocks;

FIG. 6 i a view, partly in elevation and partly in section, of a resilient connection between a partition and the kiln shell;

FIG. 7 is a fragmentary view similar to FIG. 2 but showing a heat exchanger formed of two sets of partitions;

FIG. 8 is a sectional view on the line 8-8 of FIG. 7;

FIG. 9 is a view similar to FIG. 7 showing a modified construction;

FIG. 10 is a sectional view on the line 10-10 of FIG. 9;

FIG. 11 is a view similar to FIG. 7 showing a second modified construction;

FIG. 12 is a sectional view on the line l2--12 of FIG. 11;

FIG. 13 is a fragmentary perspective View showing blocks of a modified construction;

FIG. 14 is a fragmentary perspective view showing blocks of a second modified form;

FIG. 15 is a view in perspective of blocks provided with conveying ribs; and

FIG. 16 is a view in perspective of blocks provided with flanges.

The kiln shown in the drawings includes the usual metallic shell 20, which is of generally cylindrical form and has a heat-resistant refractory lining 21. The kiln is provided with a built-inheat exchanger, which includes compartments 22 defined by radial partitions 23, each made of a stack of blocks 24 of a ceramic material, such as chamotte. In the construction shown, there are six partitions meeting at the kiln axis and the partitions have a common axial member 25 of ceramic material and of hexagonal cross-section. At the outer end of each partition, a metallic shoe 26 of U-shape fits over the outermost block 24a and the block and the shoe lie within a recess formed in the kiln lining and lined with metal plates 27.

A yoke 28 is mounted on the outside of the shell at the end of each partition and the yoke includes a crossbar 29 and a pair of bolts 30 extending through openings in the cross-bar and threaded into openings in the kiln shell. Each bolt carries a nut 31 and a lock nut 32 on its end outside the crossbar and the nuts can be adjusted to vary the position of the cross-bar relative to the shell. A member 33 having the form of a rod provided with a collar 33a has one end extending through an opening in the shell and bearing on the outer surface of the shoe 26, while the other end of the member extends into an opening 29a through the cross-bar. A spring 34- encircles the member and bears at one end against the outer face of the collar and, at the other, against the inner face of the cross-bar. In the construction illustrated, the spring is made up of a stack of dished disks and the disks are enclosed Within a cylindrical casing 35 attached to the inner surface of the cross-bar. The spring is under compression and applies compressive force to the shoe to urge the partition toward the kiln axis. By adjustment of the nuts on the bolts 30, the force exerted by the spring can be varied as desired.

In the construction illustrated, the end block 24a has a flat outer face engaging the shoe and a fiat inner face engaging the outer face of the adjacent block 241;. Also, the inner end block 240 of the stack has a fiat inner surface engaging one of the sides of the longitudinal member 25. The other contacting surfaces of the blocks are curved about axes parallel to the kiln axis and the radii of curvature of the faces facing the kiln axis, such as the surface 24d, are greater than the radii of curvatures of the surfaces facing the kiln shell, such as the surface 24a. When the blocks have this form, they are self-centering and the partitions are more stable than when the contacting surfaces of the blocks are flat. The curvature of the mating faces also avoids excessive edge pressures. If desired, the bearing faces of the axial member 25 and of the shoes and the corresponding surfaces of the blocks may be curved like the other surfaces of the blocks.

Each block preferably has concave side faces 24 and the greater thickness of the blocks at the ends than at the middle retards the movement of the material through the heat exchanger and also reduces the spill of the material, either forward or backward, so that the material moves gently and gradually out of the heat exchanger. As a result, the amount of dust entrained by the kiln gases is reduced.

The heat exchanger may be made of a single set of partitions or of two or more sets disposed at diiferent locations along the kiln axis. A typical set of partitions may have an axial length of 16" to 32 and, when two or more sets of partitions are used, the sets may be disposed close to each other or they may be separated with gaps of 16" to 32", for example, between adjacent sets.

If the material being burnt has a tendency to develop an undesirable amount of dust and if it is important that the overall length of the kiln be kept with comparatively short limits, the heat exchanger sections may be placed close together. However, if no such considerations arise, the use of sections with substantial gaps between them may be desirable because of the better mixing of hot and cold particles and of large and small particles thus obtained. Also, with the heat exchanger formed of spaced sections, there is less risk of the material damming up and then moving forward suddenly.

If the heat exchanger is made of sections placed close together, the gaps between adjacent sections may be closed by various means. Thus, the gaps between adjacent sections may be spanned by plates 36 engaging the opposite sides of the sections and held in place by bolts 37 connecting the plates and lying between the sections. In an alternative construction, the heat exchanger sections are made of blocks 38 formed at their axial ends with tongues 38a which overlap. In another alternative construction, the adjacent axial ends of the blocks 39 are channeled and a ceramic rod 40 inserted in the channel acts as a closure member.

In heat exchangers made of a plurality of sections, the partitions forming the sections may be in axial alignment or they may be angularly otfset about the kiln axis. The

latter arrangement produces turbulence in the kiln gases flowing through the kiln with consequent agitation of the material in the kiln and improved heat transfer. If the sections are close together and the gaps between them closed by plates, the extent to which adjacent partitions may be out of alignment will be small.

Instead of employing blocks of the waisted type with curved concave surfaces, such as the block 24, blocks 41 of parallelepiped shape may be employed. Such blocks may be connected to one another by dove tail connections as shown at 42 or the blocks may have tongue and groove connections shown at 43.

For some purposes, it may be desirable to provide blocks with conveying ribs on the surfaces, over which the material travels, and the blocks 44 are shown as having such ribs 4411. When it is desirable to prevent spill of the material from the partitions, they may be made of blocks 45 provided with flanges 45a at one or both ends. Ordinarily, the blocks used in a partition will be of uniform construction.

I claim:

1. A rotary kiln having a generally cylindrical shell and partition means sub-dividing the interior of the shell into longitudinal compartments, the partition means including a plurality of partitions of heat-resistant ceramic material meeting at the axis of the kiln and a radially resilient connection between the outer end of each partition and the shell, characterized in that the partitions are formed of separate blocks having contacting surfaces curved about axes generally parallel to the kiln axis, the contacting surfaces of adjacent blocks being of different radii of curvature.

2. The rotary kiln of claim 1, in which the surfaces of the blocks, which face the kiln axis, are of greater radii of curvature than the surfaces of the blocks, which face the kiln shell.

3. A rotary kiln having a generally cylindrical shell and partition means subdividing the interior of the shell into longitudinal compartments, the partition means including a plurality of partitions meeting at the axis of the kiln and a radially resilient connection between the outer end of each partition and the shell, characterized in that the partitions are formed of separate blocks of heat-resistant ceramic material having concave sides defining the compartments.

4. A rotary kiln having a generally cylindrical shell and partition means subdividing the interior of the shell into longitudinal compartments, the partition means including a plurality of partitions meeting at the axis of the kiln and a radially resilient connection between the outer end of each partition and the shell, characterized in that the partitions are made of separate blocks of heatresistant ceramic material and the blocks between the end blocks are provided at at least one end with a flange lying in a plane transverse to the kiln axis.

5. A rotary kiln having a generally cylindrical shell and partition means subdividing the interior of the shell into longitudinal compartments, the partition means including a plurality of partitions meeting at the axis of the kiln and a radially resilient connection between the outer end of each partition and the shell, characterized in that the partitions are formed of separate blocks of heat-resistant ceramic material having ribs inclined to the kiln axis extending from their sides defining the compartments.

6. The rotary kiln of claim 1, in which the partition means include a plurality of like sets of radial partitions with the partitions of each set meeting at the kiln axis and held in place by radial resilient connections between the outer end of respective partitions and the shell, the partitions of adjacent sets are substantially aligned lengthwise of the kiln, and plates attached to adjacent partitions for spanning the spaces between such adjacent partitions.

(References on following page) 5 References Cited in the file of this patent 2,105,588

UNITED STATES PATENTS 790,825 Glafke May 23, 1905 350,817 1,266,745 Wunderack May 21, 1918 527,4 7 1,275,709 Lemb Aug. 13, 191s 62 6 Davis Jan. 18, 1938 FOREIGN PATENTS Italy July 23, 1937 Belgium Apr. 15, 1954 Germany Aug. 4, 1936 

